1. Field of the Invention
The present invention relates to a grinding machine having a truing unit.
2. Description of Related Art
A grinding machine is disclosed which grinds a workpiece while controlling movement in an X direction and a Z direction of a grinding wheel (disc-like rotary grinding wheel) and which includes a truing unit so as to true a machining surface of the grinding wheel (for example, see Japanese Patent Application Publication No. 2010-253623 (JP 2010-253623 A) and Japanese Patent Application Publication No. 2010-284769 (JP 2010-284769 A)). In the grinding machine disclosed in JP 2010-253623 A, a grinding wheel and a truer are respectively rotationally driven by independent drive units. That is, the grinding wheel is rotationally driven by a grinding wheel drive motor and the truer is rotationally driven by a truer drive motor. In order to adjust surface roughness (a degree of cutting) of the grinding wheel in truing, rotational speeds of the grinding wheel and the truer are independently controlled to change a circumferential speed ratio of the grinding wheel and the truer.
In a truing unit of the grinding machine disclosed in JP 2010-284769 A, as illustrated in FIG. 11, a truer drive motor 178 and a truer 177 that is rotationally driven about a truer shaft 176 by the truer drive motor 178 are installed in a support member, for example, a spindle housing 142 of a first spindle unit. The spindle housing 142 is provided with a contact detecting mechanism 135 including a pin-like thermal displacement detector 136 that is located on a side of the truer 177 and that detects thermal displacement of a grinding wheel shaft 131 (thermal displacement of the grinding wheel shaft 131 in the Z direction) by contact and a pin-like outer circumference detector 137 that detects an outer circumferential position of the grinding wheel 132 by contact. The thermal displacement of the grinding wheel shaft 131 and the outer circumferential position of the grinding wheel 132 are detected before truing the grinding wheel 132 by the use of the truer 177, movement in the Z direction of the grinding wheel 132 is controlled on the basis of the detected thermal displacement and the detected outer circumferential position of the grinding wheel 132, and then movement in the X direction of the grinding wheel 132 is controlled. Then, the grinding wheel 132 is trued by finely moving the grinding wheel 132 in the X direction while bringing the grinding wheel 132 into contact with the truer 177 rotating by the operation of the truer drive motor 178.